Stabilization of nitroform salts



United States Patent 3,384,675 STABILIZATION 0F NITROFORM SALTS John A.Brown, Berkeley Heights, N.J., assignor to Esso Research and EngineeringCompany, a corporation of Delaware No Drawing. Filed Feb. 27, 1961, Ser.No. 92,091

6 Claims. (Cl. 260644) This invention is concerned with stabilization ofa nitroform salt of an amine by addition of a small amount of a suitablesalt additive. More particularly, it is concerned with the use ofcertain salt of a metal and of a suitable acid, either an inorganic ororganic acid, to increase the thermostability of an amine nitroformsalt, such as hydrazinium nitroformate.

The amine nitroform salts are potent oxidizers in rocl cet propellantcompositions. These salts are represented foremost by hydrazinenitroform N H -HC(NO which is also termed amino ammonium nitroformate'or hydrazinium nitroformate. Hydrazine nitroform is relatively morestable than other amine nitroform salts. Other amine nitroform salts areamino guanidine nitroform, polyamine nitroform and polyalkyleneaminenitroform salts.

The mechanism by which the amine nitroform salts are stabilized by asmall amount of a stabilizing additive is not completely understood.Studies show that the decomposition of the nitroform salts appears to beautocatalytic at elevated temperatures, e.g. 90 C. and higher. Alkalinesubstances and certain metals (e.g. Cu, Fe, Co, Ni) and their metal ionspromote the instability. Ferric oxalate induces decomposition, andcupric oxalate induces an explosion after a brief induction period. Ithas been found in accordance with the present invention that salts whichimprove the stability of the amine nitroform salts especially well aremercuric and mercurous oxalate, zinc oxalate and zinc chloride.

The data indicate that the decomposition rate of an untreated nitroformsalt, such as hydrazine nitroform, rises rapidly, as in a paraboliccurve at elevated temperatures. The decomposition rate is measured bythe cubic centimeters of gas evolved per gram of sample tested during aperiod of time at a test temperature.

Test data on the stabilization of hydrazine nitroform (HNF) are given inthe following table:

TABLE.STABILIZATION OF HNF BY SALTS AT 90 C.

Decomposition, era/gram at SIP in- HNF Specimen Percent Additive 1 Nodata.

3,384,675 Patented May 21, 1968 'ice In the foregoing table the signsindicate that the decomposition rate has increased to well above 50 cc.per gram, the gas volume being determined as under standard conditionsof temperature and pressure (ST-P).

The salts are mixed in finely divided powdered form with the nitroformsalt which is to be stabilized and the additive stabilizing salt may beused in amounts of about 1% to 5% by weight of the nitroform salt.Preferably, the amount of additive is in the range of 1 to 3 wt. percentof the nitroform salt stabilized. By using the proper stabilizingadditive in small amounts, the nitroform salt is inhibited fromdecomposing prematurely and the additive salt does not detractappreciably from the energy value of the nitroform salt when it is usedin a rocket propellant composition.

The salt additives for stabilizing the nitroform salts are useful instoring the nitroform salts and in handling of the nitroform salts andcompositing of the nitroform salts with other materials. Stabilizingsalts which are relatively free of undesirable side eifects of freeacids can be used in combination with other materials that are sensitiveto free acids. The stabilized hydrazine nitroform may be composited withvarious other high-energy propellant oxidizers, fuel ingredients andbinders. It may be encapsulated in suitable materials, e.g. compatibleresins or metals, such as aluminum.

What is claimed is:

1. Hydrazine nitroform stabilized by an admixture of about 1 to 5 wt.percent of a salt selected from the group consisting of mercurousoxalate, mercuric oxalate, zinc chloride, zinc oxalate, and leadoxalate.

2. Hydrazine nitroform stabilized by about 1 to 5 wt. percent ofmercurous oxalate admixed therewith.

3. Hydrazine nitroform stabilized by about 1 to 5 wt. percent mercuricoxalate admixed therewith.

4. Hydrazine nitroform stabilized by about 1 to 5 wt. percent of zincchloride admixed therewith.

5. Hydrazine nitroform stabilized by about 1 to 5 wt. percent of admixedlead oxalate.

6. Hydrazine nitroform stabilized by about 1 to 5 wt. percent of admixedzinc oxalate.

References Cited UNITED STATES PATENTS 3,140,317 7/1964 Groves 260644CARL D. QUARFORTH, Primary Examiner.

LEON D. ROSDOL, L. DEWAYNE RUTLEDGE,

Examiners.

J. W. WHISLER, L. A. SEBASTIAN,

Assistant Examiners.

1. HYDRAZINE NITROFORM STABILIZED BY AN ADMIXTURE OF ABOUT 1 TO 5 WT.PERCENT OF A SALT SELECTED FROM THE GROUP CONSISTING OF MERCUROUSOXALATE, MERCURIC OXALATE, ZINC CHLORIDE, ZINC OXALATE, AND LEADOXALATE.